DE69810135T2 - HYDROPHILIZED MATERIALS AND METHOD FOR THE PRODUCTION THEREOF - Google Patents

Abstract

A process is described for applying a solid coating onto a surface of an article. The surface of an article has a first physical property measurable as a degree of hydrophobicity and/or hydrophilicity. A liquid coating of an oxidizable material containing at least one element other than carbon, hydrogen, oxygen and nitrogen is applied onto the surface of the article. The oxidizable material is oxidized on the surface to attach an oxidized material having said at least one element other than carbon, oxygen, nitrogen and hydrogen onto said surface. This process thereby changes the first physical property with respect to its hydrophobicity and/or hydrophilicity. The process is relatively gentle to the underlying surface, at least in part because of the moderate temperatures which may be used for oxidation, and a wide range of properties may be provided onto the surface by appropriate selection and/or mixing of the liquid material and selection of the surface. The process is particularly useful with particulate materials.

Description

Background of the invention 1. Field of the invention

The present invention relates to the formation of oxide coatings on surfaces of materials, in particular the formation of coatings with controlled hydrophilic/hydrophobic surface properties, in particular by forming hydrophilic oxide coatings from inorganic, semi-metallic and/or metallic oxides and more particularly the formation of these controlled coatings, e.g. from a hydrophilic oxide, on particles in order to adjust the surface properties and/or chemical properties of the particles. The particles may comprise materials such as fillers, pigments, lake dyes, catalysts, matting agents, optical diffusers, reinforcing agents, magnetic particles, catalysts, reflective materials, film or foil surfaces, fibers, filaments and numerous other forms of materials, and in particular particulate additives.

2. State of the art

Particles are conventionally and conveniently added to many different types of compositions and products where the particles are intended to retain their particulate form after manufacture or completion of the product: Applications for particulate products include a wide variety of technical uses such as fillers, colorants (e.g. pigments and lake dyes), matting agents, anti-slip agents, optical diffusion agents, reinforcing agents, viscosity modifiers, reflective particles, magnetic particles, carriers for other compounds and materials and other types of composition additives. There are a number of difficulties which have long existed in the use of particles in other preparations. The composition of the particle may react with components in the preparation and interfere with a desired activity of a component; reaction of a component of the preparation with the particle may adversely affect the properties (physical or chemical) of the particle; the particle may be incompatible with the preparation or may not be suitable for forming stable dispersions or suspensions.; or the particles may agglomerate within the preparation and not reach the appropriate size. Various techniques and chemical measures have been used for years to overcome these difficulties.

Among the techniques used to overcome these difficulties are the application of coatings to the surface of the particles, the use of coupling agents on the surface of the particles, the physical modification of the surface of the particles, the chemical modification of the existing composition on the surface of the particles and/or the modification of the formulation to tailor the particle. The latter technique represents one of the least desirable methods of controlling the behavior of the particles in the formulation, since it requires a fundamental or at least patchwork change in the composition, which may also alter its essential properties. Similarly, coatings on the surface of the particles or a conversion of materials (e.g. coupling agents) on the surface may affect more than the mere hydrophilic/hydrophobic balance of the properties of the surface and may even impart undesirable functional properties to the particle surface that directly affect the behavior of the composition. Physical modification of the surface of the particles can easily affect their optical properties, and the fabrication of coatings can be difficult and expensive, with results that can vary widely from one particle type to another.

Zinc oxide is a special pigment that has received considerable attention for its commercial application in coatings applied thereto. As described in U.S. Patent 5,486,631, zinc oxide is coated with organic oils, such as the organic oil tri-(octyldodecyl) citrate, to obtain a stable dispersion of zinc oxide that can be used in sunscreen filters. The coating with the organic oil is not permanent and therefore not durable because the oil does not react with itself to form a coating or with the zinc oxide itself. The oil also disrupts the uniformity of the zinc oxide particles themselves when they are distributed on the skin in sunscreen preparations. This patent (5,486,631) describes the use of a special type of reactive silicone to coat the surface of To hydrophobize zinc oxide particles. Silicone compounds of the following formula are specified:

where Me is methyl,

R represents an alkyl group having 1 to 10 carbon atoms,

R' is methyl or ethyl and

a is an integer in the range up to 12.

It is at least noteworthy that these types of compounds are used in the prior art as represented by this document (5 4866 631) to hydrophobize surfaces, whereas according to the invention it is possible to increase the hydrophilic nature of the surfaces and even to make them hydrophilic by using the process according to the invention which is different from the prior art.

The special silicone compounds are mixed with the zinc oxide particles and then the mixture is heated to a temperature of 40 to 100°C for 2 to 10 hours. The silicone compound is intended to create direct bonds between the silicon atom and the zinc oxide crystals, whereby the other valencies of the silicon atom are of course saturated by the original groups of the special silicone compounds.

US Patent 5,536,492 describes the use of hydrophobized zinc oxide particles, such as those prepared in US Patent 5,486,631, in sunscreen products applied to the skin.

US Patents 5,458,681 and 5,368,639 describe pigments treated with an organosilicon compound, a process for preparing such treated pigments and cosmetic compositions prepared with such treated pigments. Linear, reactive alkylpolysiloxanes with specific substituent groups (e.g. amino, imino, halogen, hydroxyl and/or alkoxy groups) are oriented by a heat treatment and adsorbed on the surface of a pigment or extender. The alkylpolysiloxane is said to have a specific polymerization range of 25 to 100 and a Mg/Mn ratio of 1.0 to 1.3. The silicone should adhere firmly to the surface of the pigment.

Coatings of organometallic compounds, organic non-metallic compounds, inorganic oxides and inorganic non-oxide materials are widely used to form abrasion-resistant and/or solvent-resistant coatings on surfaces, including the surfaces of polymers. Materials used for this purpose include a wide range of materials including (but not limited to) acrylates, polysiloxanes, ambifunctional polysilanes, esters of metals (e.g., esters of titanium, aluminum, zirconium, and the like) alone or in combination with other ingredients such as ambifunctional silanes (see, e.g., U.S. Patent 4,084,021).

Silane and titanate compounds are also known from the general literature as adhesives or adhesive moieties for chemically bonding materials together, including the bonding of specific functional moieties to specific surfaces. In this regard, Tamon, Okano, Katsunori Tsukiyama, Hisotoshi Konishi and Hitsuo Kiji in "Versatile Polymer-Bound Rhodium Catalysts; Facile Hydrogenation of Aromatic Compounds in the Liquid Phase", Chemistry Letters, (1982), pp. 603-606, state that phosphino groups are bonded to silica (glass) surfaces by reacting an alpha-phosphinopropyltrimethoxyalkane with the glass to form a bonded moiety with an alpha-phosphinopropyl group bonded to the glass via a trisiloxy bond.

Amphoteric/ambibifunctional compounds of silanes and titanates, as well as other classes of bifunctional compounds, can also be used as coupling agents, with the different end groups selected for appropriate reactions to assist in the bonding or stabilization of two dissimilar surfaces or materials. Of particular interest to the practice of the invention is U.S. Patent 4,756,906, which describes a tunable cosmetic composition. In discussing the prior art, it describes the use of adsorption (including chemisorption) by Van der Waals forces, dipole-dipole attraction, or hydrogen bonds to associate additives with the cosmetic composition and coupling agents. Titanate and silane coupling agents are comprehensively described. The list and formulas for Materials within these classes in columns 5 and 6 as well as the classes of pigments described in columns 6 and 7 are hereby incorporated by reference.

US Patent 5,520,952 describes a process for producing protective film coatings, particularly on electronic components and devices. The process involves applying a liquid coating composition to a surface, the major component of the coating composition comprising a partial cohydrolysis condensation product of a tetraalkoxysilane and a functional alkoxysilane (e.g., tetraethoxysilane or 3-methacryloxypropyltrimethoxysilane, respectively). The coated article is heated to cure the composition. Finely divided inorganic filler (e.g., colloidal silicon dioxide) may be added to the liquid coating composition to further increase the hardness of the cured coating. U.S. Patent 5,496,402, which was co-assigned with U.S. Patent 5,520,952, describes stable coating compositions containing two different hydrolyzable silanes, one of them a triestersilane and the other a tetraestersilane. A third, co-assigned patent, namely U.S. Patent 4,865,649, also describes a coating solution for forming a silica-based coating film, the coating solution containing an organic solution of a hydrolyzate of an alkoxysilane mixture of at least two different types of di-, tri- and tetraalkoxysilane compounds in a certain molar ratio. The coating compositions are cured in the presence of water without the need for an acid catalyst to effect the cohydrolysis of the silanes. Another related patent, US-4,277,525, describes liquid coating compositions for forming silica coating films, the coating composition containing an alkoxy-containing silane, a lower carboxylic acid and an alcohol, in the presence of a reaction accelerator (which is an acid other than the carboxylic acid).

US Patent 5,344,751 describes an antistatic protective coating comprising a mixture of sodium metasilicate, a silica sol and a silane coupling agent. Similar Compositions containing orthosilicates are also known from the patent literature.

US Patent 4,455,205 discloses that UV-curable coatings containing a photoinitiator, the hydrolysis product of silyl acrylate and aqueous colloidal silicon dioxide (also in combination with a polyfunctional acrylate) produce adhesive and abrasion-resistant coatings, particularly on polycarbonate resins.

Abrasion resistant coatings and metal oxide coatings have also been applied to surfaces by vapor deposition processes, where metal and oxygen (and/or other reactive materials such as sulfur) are vaporized and reacted/deposited onto the surfaces to form coatings. Apparatus and methods for this type of coating are described, for example, in U.S. Patents 4,430,366 and 4,405,678. These coatings may also have gradations in their relative atomic distribution of materials within the vapor deposited layers.

It is known in the art that pigments are desirably provided with coatings to protect them from preparations with which they are mixed, as already stated above. US Patent 5,482,547 describes the application of a tough coating of an alkyl silicate to pigments, the coating being fixed to the surface of the pigment by adsorption of an alkyl silicate onto a layer which covers the surface of the pigment particles and consists essentially of partially hydrolyzed organic compounds of a specific formula containing elements of Groups IVa or IVb and of chelates of a specific formula, the chelates being titanium or tin chelates. The alkyl silicate can be hydrolyzed before, during or after adsorption. The result of this special coating is said to be good gloss and good rheological properties.

Each of these processes and other commercial processes have their respective advantages and disadvantages. A surprising aspect of this field of technology is that even when similar starting materials are used for the different processes, different products and/or different properties in the final article result, which is due to variations in the conditions Alternative coatings, coating solutions and coating processes that provide a wider and different range of properties are still desired.

Summary of the invention

The present invention relates to the application of a coating with specially designed hydrophilic/hydrophobic properties to the surface of objects by oxidative means. The surfaces are particularly advantageously the surfaces of particles. The coating is particularly preferred if it contains inorganic oxymetallic bonds of units MyOx (where M is a metal or metalloid, y is the number of M atoms and x is the number of oxygen atoms in the bond or in the bond units), such bonds including, for example, units such as SiOx, ZnOx, TiOx, AlOx, SnOx, MnOx, MgOx and the like (other materials are listed below). The coatings are applied by forming a liquid coating comprising an oxidizable inorganic/metallic compound on the particles or surface and then oxidizing the metallic compound to form the coating on the surface. The coating can be continuous or discontinuous, which usually depends on the area of liquid coverage on the particle before oxidation.

Detailed description of the invention

Surfaces are described that have coatings on them that modify, control and/or adjust the hydrophobic/hydrophilic properties of the surface of the underlying material. Since surfaces of specific compositions or materials have their own special properties, including surface charge and properties related to their affinity for different types of materials (e.g. hydrophobicity, hydrophilicity, oleophobicity and oleophilicity, as well as polar and non-polar attraction), it is often desirable to have treatments and coatings that can affect and/or modify these inherent properties. These treatments can enable wider application or improved application of the materials in different environments.

The basic method according to the invention comprises applying a liquid to a surface having a first physical property measurable as a degree of hydrophobicity and/or hydrophilicity, wherein the liquid coating contains, consists essentially of, or consists of a first compound having an inorganic oxidizable group or moiety, and then oxidizing said first compound to form a second compound bound to said surface, said second compound altering said first physical property. In most cases, the first physical property alters toward greater hydrophilicity, depending upon the essential nature of the first compound used. Preferred compounds include inorganic or, in particular, metallic metalloid or semi-metallic ester-containing compounds, such as the oxides MxOy (as stated above) and, in particular, silicon compounds, such as silanes (e.g. RmSi[OR¹]n), ie compounds in which R is an organic group (preferably bonded to the Si atom via a carbon atom), halogen or hydrogen, R¹ is hydrogen or an organic group, such as alkyl, aryl or a heterocycle and preferably alkyl having 1 to 4 carbon atoms, m has the value 0, 1, 2 or 3 and n has the value 1, 2, 3 or 4; titanate counterparts of the silanes, such as RmTi[OR¹]n, in which R, R¹, m and n have the meanings defined above; and any other oxidizable metal or semimetal compounds of the general formula RmM[R¹]n, in which M is a metal or semimetal selected, for example, from the group Si, Ti, Zn, Al, Sn, Fe, Cu, Zr, B, Mg, Mn, W, Sb, Au, Ag, Cr and the like, R and R¹ have the meanings defined above, m plus n corresponds to the valence state of M and n must have at least the value 1. In addition to the preferred silanes, which are preferred primarily because of their ease of use and ready commercial availability, silicon compounds such as silazanes, cyclic siloxanes, siloxane dimers, siloxane trimers, liquid silanes and tris-(alkoxysiloxy)-3-methacryloxyalkylsilanes (less preferred) can be used in the practice of the invention.

In addition to these special classes of compounds and metals/metalloids and in addition to monometallic, monometalloid compounds as starting materials, dimetallic (with two different metal/metalloid atoms, bimetallic (with two identical metal/metalloid atoms in the compound), heterometallic (having a metal atom and a metalloid atom in the same compound), dimetalloid and bimetalloid compounds, and mixtures of any of these groups of compounds. Mixtures of the compounds offer special possibilities for evenly distributing different properties across a surface or for equalizing (evening out) properties across the surface. A very wide variety of these classes of oxidizable metal or metalloid compounds are commercially available; See, for example, the list of compounds in the 1996 Chemical Catalog of Gelest, Inc. (e.g., pages 287 for a general description of heterometallic or heterometalloid alkoxides, including alkali metal combinations; and especially pages 21-217; 220-221, 231-233, and 258-265) and the 1994 PCR Catalog, Incorporated General Catalog of "Chemicals for Research Scientists" (especially pages 192-193 and 198-199).

Germanium compounds prove to be functionally similar to silicon compounds in the practice of the invention. A large number of such compounds are listed in the aforementioned Gelest catalog of 1996, in particular on pages 216-217.

Similarly, oxidizable tin compounds as described above represent another class of compounds which are equivalent to silicon compounds in the practice of the present invention. Within this class there are numerous commercially available alternatives; see, for example, pages 258-264 of the 1996 Chemical Catalog of Gelest, Inc. Examples of R (as shown in the silicon compound of the above formula and equally applicable to corresponding groups bonded to other metal or metalloid atoms in the oxidizable compounds of the present invention) will be apparent to those skilled in the art. They may be functional groups (e.g., with specific reactivity) or relatively non-reactive groups which provide valuable physical properties when the material is applied to the surface prior to oxidation or, less likely, which leave a residue after oxidation. Such R groups include aliphatic and aromatic groups, such as alkyl groups, alkyl ester groups, poly(oxyalkylene) groups, phenyl groups, naphthyl groups, H, hetero groups (e.g. thioethers), functionally terminal groups, such as aminoalkyl, epoxyalkyl, carboxyalkyl, whereby Halogen atoms such as I, Br, Cl and F are possible (but these are less preferred because of the halogen products including halogen acids) and the like. R¹ can be any oxidizable group, e.g. an ester group, including those having their own functionality at the distal end (relative to the bonding site) of the group. Such R¹ groups form ester and ester-type groups upon bonding, so that R¹ actually represents an aliphatic or aromatic group, e.g. R, but is preferably limited to aliphatic groups having 1 to 20 carbon atoms, especially 1 to 10 carbon atoms, and most particularly 1 to 4 carbon atoms for aliphatic groups and 1 to 10 carbon atoms for aromatic groups. With respect to silicon-based compounds, representative examples are the silicone compounds described in U.S. Patent 5,486,631, the reactive silanes described in U.S. Patent 4,084,021, and numerous other commercially available silicon compounds that can be oxidized, particularly at temperatures of 250 to 600°C, and most particularly at temperatures of 350 to 500°C. Furthermore, it is possible to employ low temperature oxidation environments, for example, in the presence of oxidizing additives, or in oxidizing steam conditions, or in the use of supported aerobic catalysts or accelerators, to enable low temperature oxidation on surfaces that would not normally withstand the temperatures used to oxidize silicon-containing materials (or other classes of materials). The oxidation product of this reaction may actually cause a direct chemical bond to the substrate composition or may merely result in a strong physical adhesion, although the former result is more likely to be the result of a washing process of the surfaces after the oxidation process.

The remaining classes of compounds include the counterparts of these compounds (i.e. silicon is replaced by the other elements), such as titanate esters, zirconium esters and other metal or non-metal esters. Mixtures of the various oxidizable compounds can be used as suggested above to give particularly favorable results, with variations or mixtures of properties on the surfaces, discontinuous regions of special surfaces, mixtures (equalization of properties) and the like.

A non-exhaustive list of compounds suitable for the practice of the invention is given below. They are materials such as:

Isobutyltrimethoxysilane, aminopropyltriethoxysilane, aminopropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, n-(2-aminoethyl)-3-aminopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, n-octyltriethoxysilane, hexamethyldisilazane, diethylsilane, vinyldimethylchlorosilane, vinylmethyldichlorosilane, vinylmethyldimethoxysilane , tetrakis-[1-methoxy-2-propoxy ]-silane, triethylchlorosilane, vinylmethyldiethoxysilane, vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, dimethyldiethoxysilane, hexamethyldisilazane, divinyltetramethyldisilazane, tetramethyldisilazane, heptamethyldisilazane, tris-[(trifluoropropyl)-methyl]-cyclotrisiloxane, methylvinylcyclotetrasiloxane, 1,3,5,7- Tetramethylcyclotetrasiloxane, 1,3,5,7,9-pentamethylcyclopentasiloxane, - hexamethyldisiloxane, divinyltetramethyldisiloxane, divinyltetramethyldisiloxane (high purity), tetramethyldisiloxane, 1,3-bis-(3-aminopropyl)-tetramethyldisiloxane, heptamethyltrisiloxane, chlorinated siloxane, 1,3- Bis-(aminopropyl)-tetramethyldisiloxane, bis-(3-aminopropyl)-polydimethylsiloxane, bis-(3-aminopropoxy)-polydimethylsiloxane, diethoxy-polydiemthylsiloxane, tris-(trimethylsiloxy)-3-methacryloxypropylsilane, tetraisopropoxygermanium, tetrakis-(trimethylsiloxygermanium), Tetramethoxygermanium, tetramethylgermanium, tetrapentylgermanium, tetraphenylgermanium, tetra-n-propylgermanium, tetra-p-tolylgermanium, triallylfluorogermanium, tri-n-butylacetoxygermanium, tetraphenyltin, tetravinyltin, tin(II) acetate; Tin(IV) acetate, tin acetylacetonate, tin tert-butoxide, tin(II) chloride, anhydrous tin(II) chloride, tin(IV) chloride dihydrate, anhydrous tin(II) ethoxide, tin( II)-fluoride, tetramethyltin, tetran-octyltin, tetra-n-pentyltin, tetraethyltin, tetraisopropoxytin-isopropanol adduct, tetraisopropyltin, tetrakis-(diethylamino)-tin, tetrakis-(dimethylamino)-tin, potassium stannate trihydrate, sodium stannate trihydrate, sodium tin ethoxide , tin(IV) chloride, tetraacetoxytin, tetraallyltin, tetra-tert-butoxytin, tetra-n-butyltin. Methacryloxytri-n-butyltin, methyltrichlorotin, phenylethynyltri-n-butyltin, phenyltri-n-butyltin, phenyltrichlorotin, divinyldi-n- butyltin, 1-ethoxyvinyl-tri-n-butyltin, ethynyltri-n-butyltin, hexabutyldistannoxane, hexa-n-butylditin, hexamethylditin, dimethylhydroxy-(oleate)-tin, dimethyltin oxide, dioctyldichlorotin, dioctyldilaurlytin, dioctyldineodecanoatetin, at)- tin, dioctyltin oxide, diphenyldichlorotin, allyltrichlorogermanium, allyltriethylgermanium, allyltrimethylgermanium, 3-aminopropyltributylgermanium, ammonium hexafluorogermanate, ammonium tris-(oxalate)-germanate, benzyltrichlorgermanium, bis-[bis-(trimethylsilyl)-amino]-germanium II, bis-(chloromethyl) -dimethylgermanium, Bismuth germanate, bromomethyltribromogermanium, bromotrimethylgermanium, tetra-n-butylgermanium, tetraethoxygermanium and tetraethylgermanium.

Preferred silicon compounds according to the invention can be represented by the following formula:

where Me represents a methyl group,

R represents an organic group and preferably an alkyl group having i to 10 carbon atoms,

R' represents an alkyl or aryl group and preferably a methyl or ethyl group and

a is an integer in the range 4 to 12.

Counterparts of these materials in which Me is replaced by other organic groups, particularly alkyl groups, are suitable for the practice of the invention, as are the other listed elemental counterparts (e.g., the titanium and germanium counterparts and the like of silicon).

The practice of the invention is based on the fact that the prior art accepts or even recommends the substitution of groups within these chemical formulas. In this regard, when the term "group" is used to describe a chemical material or functionality, the description of this term specifically includes a conventional substitution. For example, when an alkyl group is mentioned, this includes not only alkyl radicals such as methyl, ethyl, isobutyl, tert-butyl, isooctyl and dodecyl, but also alkyl radicals with conventional substitutions as known from the relevant prior art, e.g. hydroxymethyl, 1- or 2-haloethyl, omega-cyanobutyl, propylsulfonate and the like, with substituent groups such as amino, carboxy and acyl groups being accepted in accordance with common practice in the art. When the term "radical" is used, e.g. in the term "alkyl radical", this term means only the strict definition of alkyl (or other modified radicals) without substitution being permitted.

The substrates to which the compositions of the invention can be applied and oxidized into coatings are generally limited only by the ability of the substrate to withstand the temperatures used in the oxidation process. Metals, metal oxides, generally inorganic oxides, glasses, ceramics, composites, pigments (organic or inorganic), enamels, catalysts, reflective particles, magnetic particles, radiation absorbing particles, flat surfaces, shaped surfaces, structural elements and the like can all be advantageously treated with the compositions and methods of the invention. Since the composition of the invention can be easily controlled with respect to the thickness or continuity of the fatty coating, a variety of other applications and properties can be achieved. For example, by controlling the amount of liquid coating on the surface, the continuity of the liquid coating, the thickness of the liquid coating, and the like, similar properties in the fatty oxidized materials can also be controlled. If the coated substrate was catalytic in nature, the degree of porosity allowed in the coating can control the degree of exposure of the catalyst. If the underlying substrate was highly hydrophobic, the specific degree of hydrophilicity/hydrophobicity of the product can be controlled by controlling the specific percentage of surface area, i.e., the exposed underlying material or coating formed by the oxidation process.

In compounding technology, i.e. in fields of technology where materials are prepared into related but different end products, it is often the case that a considerable amount of time has to be spent on reformulating compositions due to changes in non-functional components. For example, in the cosmetic industry, the replacement of a pigment in a cosmetic composition by another pigment alter the physical properties of the final product and even render the preparation unsuitable due to these changes in properties. These changes are often due to different chemical and/or physical properties (usually not mere size differences) between pigments. In particular, a difference in hydrophobicity/hydrophilicity between different pigments may prevent the direct substitution of pigments (which are otherwise considered to be substantially identical) in compositions. For example, when developing a novel lipstick base or an eye shadow base, each colour has to be formulated separately, not because of colour effects, but because of chemical/physical interactions between the various colouring agents (e.g. the pigments) and the base. This adds significantly to the costs of introducing new cosmetic compositions without offering any specific advantages in the slight variations in compositions which often have to be made in order to use different pigments.

The present invention enables one to stockpile pigments having different colors or color effects (e.g., fluorescence, luminescence, pearlescence, and the like) but which appear identical in composition and to the manufacturer in terms of the physical properties of the pigment (except possibly size). This enables the manufacturer to stockpile pigments (having substantially indistinguishable physical properties) and create formulations and preparations from a single base or standard composition without the need for reformulation each time a color change occurs. This is accomplished according to the practice of the invention by employing different pigments having different colors or color effects, applying an oxidizable liquid coating according to the practice of the invention, oxidizing the liquid coating composition to form a coating on each separate batch of pigments having a particular range of physical properties (particularly with respect to hydrophobicity/hydrophilicity), and maintaining a stock of these different pigments. A base or standard compounding preparation is created. Various color preparations are created by incorporating the specifically desired pigments with their substantially identical hydrophobic/hydrophilic surface properties into the standard compounding formulation. Since the various color pigments are physically and chemically essentially identical to the formulation, no variation of the formulation is necessary other than determining the concentration of pigment required to achieve the desired color density or saturation for the particular color.

A further alternative in the practice of the invention is to provide an oxidizing environment during the oxidation step. This can be done by appropriate choice of oxidizable compounds, conducting the step in air, in an environment with an available oxidizing agent or in an oxygen-rich environment, by providing compounds that release or provide oxygen (e.g. peroxides, including hydrogen peroxide), and by other techniques familiar to the chemist.

The liquid may be applied to the surface by any convenient method, including (but not limited to) conventional methods for applying liquid coatings such as dipping, spraying, spreading, printing, gravure printing, screen printing, mixing (particles with a liquid), cyclone coating, and numerous other available methods.

The oxidation process can also be used to control the agglomeration of particles rather than allowing the particles to seek their own agglomeration state. For some compositions, controlled agglomeration may be desirable as opposed to the complete absence of agglomeration.

Furthermore, according to the practice of the invention, it is possible to provide patterned or image distributions of the formed inorganic oxides (e.g., silicon dioxide) on a surface by first creating a predetermined pattern of an oxidizable compound on the surface of the material and then oxidizing the oxidizable material to form a predetermined distribution of residues on the surface. Although a desirable aspect of the present invention is to be able to apply colorless coatings to surfaces so that the underlying colors are not affected, the oxidation products can also be chosen to produce colours. In this way, special colours can be added as complete coatings (continuous coatings) or as patterns, e.g. discontinuous coatings.

Several different types of particles were coated with a silane of the following formula

where R is alkyl of 1-10 carbon atoms, R' is methyl or ethyl and a is an integer having a value of 4-12. The silane coated particles were then heated to 500°C under ambient conditions (open atmosphere) for 1 hour.

Zeta potential measurements were taken to document the changes in surface properties. As controls, we also heated the uncoated particles and performed zeta potential measurements on them as well. The two particles tested were iron oxide and mica.

Black iron oxide, no prior surface treatment Heating to 500ºC, no surface treatment

pH ZP (mv)

3.70 29.5

4.40 30.23

5.02 28.00

8.05 4.97

9.13 -16.00

10.5 -21.10

Heating to 500ºC after applying 10% silicone

pH ZP (mv)

3.20 10.56

3.84 0.02

4.12 -5.47

4.6 -6.57

5.14 -9.26

5.18 -17.40

10.67 -29.40

It should be noted that the zeta potential (measurement of surface charge) became negative between pH 8.05 and 9.13 for the untreated particle and at much lower pH values (around 4) for the treated particle. Pure silicon dioxide has a negative zeta potential at all of these pH values. This shows quite convincingly that by applying our method we applied a sufficient amount of silicon dioxide to the surface to change the zeta potential. In practice, there are numerous possible applications for this. For example, the positively charged particles of untreated iron oxide are difficult to use in anionic systems (the vast majority of emulsifiers are anionic). By treating the surface, we made the particles anionic (at pH values used in cosmetics) and thereby improved their suitability.

Mica without surface treatment before coating Mica heated to 500ºC without treatment

pH ZP (mv)

3.5 -6.39

4.8 -22.6

6.8 -27.61

10.0 -36.55

Mica treated with 10% silicone heated to 500ºC

pH ZP (mv)

3.5 -20.40

5.70 -33.47

8.9 -35.80

10.10 -38.21

Claims (15)

1. A method for applying a solid coating to a surface of a solid object, the surface of an object having a first physical property measurable as a degree of hydrophobicity and/or hydrophilicity, comprising the steps of: applying to the surface of the object a liquid coating of an oxidizable material comprising at least one element other than carbon, hydrogen, oxygen or nitrogen and comprising a silane or a metal ester represented by the following formula: RmM[OR¹]n, where M is one of the elements Si, Ti, Zn, Al, Sn, Fe, Cu, Zr, B, Mg, Mn, W, Sb, Ge, Au, Ag and Cr, where R is an organic group, a halogen or hydrogen, R¹ is H or an organic group, m plus n is equal to the valence state of M, and n is at least 1, subsequently oxidizing the oxidizable material so that a material containing the element M adheres to the surface, and thereby changing the first physical property with regard to its hydrophobicity and/or hydrophilicity. 2. The method of claim 1, wherein the surface has a color and oxidizing and applying a material to the surface does not change the color of the surface by more than 0.3 units of optical density at any wavelength between 410 and 700 nm when observed by reflection or transmission. 3. The method of claim 1, wherein the surface has a color and oxidizing and applying a material to the surface does not change the color of the surface by more than 0.1 units of optical density at any wavelength between 410 and 700 nm when observed by reflection or transmission. 4. A method for preparing mixtures comprising the steps of: preparing a supply of more than two different particulate materials containing coated particles, the coating of the particles being formed by the method of claim 1, and providing a first physical property which is defined as the degree of Hydrophobicity and/or hydrophilicity is measurable at a coating surface, wherein the stock of substances has similar measurable values with respect to the first property of hydrophobicity or hydrophilicity, providing a standard binder composition for use with the substances, and selecting at least one type of the substances from the stock for mixing into the standard binder composition, and mixing at least one type of the substances from the stock into the standard binder composition. 5. The method according to claim 4, wherein the substances comprise at least two different pigments. 6. The method of claim 5, wherein the more than two particulate materials comprise more than two pigments whose numerical average particle size differs from one another by no more than +0.2%. 7. The method of claim 4, wherein each particle surface of the more than two different particulate materials has a color, and the coating formed by oxidizing and applying the material to the surface does not change the color of the surface by more than 0.3 units of optical density at any wavelength between 410 and 700 nm when observed by reflection or transmission. 8. The method of claim 4, wherein the coating was applied by a method for applying a solid coating to a surface of the particles, wherein each particle surface has a first physical property measurable as a degree of hydrophobicity and/or hydrophilicity, comprising the steps of: applying a liquid coating of an oxidizable material to the surface of the particles, wherein the oxidizable material contains an element that is neither carbon, hydrogen, oxygen nor nitrogen and comprises a silane or a metal ester represented by the following formula: RmM[OR¹]n, where M is one of the elements Si, Ti, Zn, Al, Sn, Fe, Cu, Zr, B, Mg, Mn, W, Sb, Ge, Au, Ag and Cr, where R is an organic group, a halogen or hydrogen, R¹ is H or an organic group, m plus n is equal to the valence state of M, and n is at least 1, subsequently oxidizing the oxidizable material so that a material containing the element M adheres to the surface, and thereby changing the first physical property with regard to its hydrophobicity and/or hydrophilicity. 9. The method of claim 8, wherein the surface of a particle has a color, and the oxidation and application of a substance to the surface of a particle does not change the color of the particle surface by more than 0.3 units of optical density at any wavelength between 410 and 700 nm when observed by either reflection or transmission. 10. The method of claim 8, wherein the surface of a particle has a color, and the oxidation and application of a substance to the surface of a particle does not change the color of the particle surface by more than 0.1 units of optical density at any wavelength between 410 and 700 nm when observed by either reflection or transmission. 11. The process according to claim 1 or 8, wherein R is an aliphatic organic group. 12. The process according to claim 1 or 11, wherein R¹ is an aliphatic or aromatic group. 13. The process of claim 1, wherein R¹ is an alkyl group, and 14. The process of claim 11, wherein R¹ is an alkyl group having 1 to 10 carbon atoms. 15. The method of claim 1 or 8, wherein M is silicon.